This invention relates to feeding sheets between a pair of rollers.
When feeding articles such as punched cards or envelopes which are only a few inches wide, a single pair of rollers of about one inch in width has been found sufficient to forward the articles along their path.
We have discovered that it is not possible to forward very wide sheets between a pair of rollers of this size, as the sheets very easily become skewed so that they do not follow the desired sheet feed path. A pair of very long rollers would be ruled out on the grounds of cost.
In accordance with the present invention, we provide a plurality of rollers mounted on a shaft and forming a nip with a second roller or rollers mounted for rotation about an axis substantially parallel to said shaft, together with other features which will be described below.
It is usual to form the driving surfaces of such feed rollers of resilient material in order to increase friction between the rollers and the sheet, and we have found it convenient to form such surfaces by moulding onto a central shaft or central bearing to fit on a shaft. It is difficult to mould such rollers with their surfaces accurately concentric with the shaft or bearing, so that two pairs of rollers formed in this way may provide an uneven drive to a sheet fed between the rollers of the pairs.
In order to accommodate sheets of different thicknesses and to provide an approximately constant pressure between the rollers of a pair whatever the thickness of a sheet passing between them, it has been proposed to mount the shaft carrying one pinch roller for movement towards and away from the shaft carrying the other pinch roller of a pair and to bias the two shafts together. British Patent Specification No. 922780 discloses in FIG. 3 such an arrangement, but in connection with a single pinch roller in the form of a friction disc with a spring mounting at each end of the shaft supporting the friction disc. This arrangement has been tried in connection with a plurality of sets of pinch rollers mounted across the width of a wide sheet, but it has been found that with moulded pinch rollers which may not be accurately concentric, feeding of a wide sheet without skewing is impossible.